1. Field of the Invention
This invention relates to the structure of flat display panels.
The present application claims priority from Japanese Application No. 2004-172956, the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, flat display panels include a PDP (Plasma Display Panel), an FED (Field Emission Display) and the like.
A color PDP is structured as illustrated in FIG. 1. That is, row electrode pairs (X, Y), a dielectric layer 2 covering the row electrode pairs (X, Y) and a protective layer 3 covering the dielectric layer 2 are provided on the rear-facing face of a front glass substrate 1. The front glass substrate 1 is placed opposite a back glass substrate 4 with the discharge space in between. Column electrodes D are provided on the inner face of the back glass substrate 4 and extend in a direction at right angles to the row electrode pairs (X, Y) so as to form discharge cells C in matrix form at positions corresponding to the intersections with the row electrode pairs (X, Y) in the discharge space. Further, on the inner face of the back glass substrate 4, a column-electrode protective layer 5 covers the column electrodes D. A partition wall unit 6 is formed on the column-electrode protective layer 5 to partition the discharge space into the discharge cells C. Red-, Green- and Blue-colored phosphor layers 7 are provided individually in the discharge cells C. The discharge space is filled with a discharge gas including xenon gas.
For generating an image on the panel surface in accordance with a video signal, the PDP initiates a discharge (sustaining discharge) between opposed transparent electrodes Xa and Ya on either side of a discharge gap g in each row electrode pair (X, Y) in order to generate vacuum ultraviolet light from the xenon gas in the discharge gas. The vacuum ultraviolet light excites the phosphor layers 7 and causes them to individually emit red-, green- and blue-colored visible light.
In the structure of the FED illustrated in FIG. 2, an anode electrode Ep and a transparent phosphor layer 11 are formed on the rear-facing face of a front glass substrate 10. A cathode electrode En, an insulation layer 13 covering the cathode electrode En, and a gate electrode Eg formed on the insulation layer 13 are formed on the front-facing face of a back glass substrate 12. The vacuum space between the front glass substrate 10 and the back glass substrate 12 is partitioned into pixels by a partition wall unit 14.
Regarding the FED, in the vacuum space in each pixel, drive voltage is applied between the anode electrode Ep and the cathode electrode En to generate an electric field enabling an electron beam to travel from the cathode electrode En toward the anode electrode Ep. The electron beam is accelerated by a gate electrode Eg to come into collision with the phosphor layer 11, whereby the phosphor layer 11 emits visible light to generate an image on the panel surface.
The PDP structured as described earlier needs a drive voltage of from 200V to 300V, for example, for enhancement of luminous efficiency. For this purpose, what is required, for example, is a semiconductor device for a high-voltage drive which is typically expensive. Such a requirement gives rise to the problem of high manufacturing costs.
The FED needs high voltage for its drive and therefore includes a complicated and high-cost drive circuit in the display device. Further, a high-velocity electron beam ionizes contaminated gas remaining within the panel. The ion impact at the time of this ionization causes wear and tear on the microchip array provided for generating the electron beam. As a result, the FED has the problem of a short lifetime.
The flat display panel, which is conventionally suggested in order to solve the problems associated with the structure of the PDP and FED, has the back substrate provided with an electron-emitting source emitting electrons by heat or an electric field, and the front substrate provided with anode electrodes accelerating the electron beam emitted from the electron-emitting source and phosphor layers covering the anode electrodes. The space between the front substrate and the back substrate is filled with xenon gas.
A conventional flat display panel structured as described above is disclosed in Japanese unexamined patent publication 2001-6565, for example.
In the conventional flat display panel, the electrons emitted from the electron-emitting source provided on the back substrate are accelerated by a voltage applied to the anode electrode. The accelerated electrons directly excite the xenon gas filling the space defined between the front substrate and the back substrate to cause the xenon gas to emit ultraviolet light. The ultraviolet light excites the phosphor layers formed on the front substrate to cause the phosphor layers to emit visible light, resulting in the generation of an image.
However, the conventional flat display panel has the following problems.
In the conventional flat display panel, the electrons emitted from the electron-emitting source are accelerated by anode voltage in the space filled with xenon gas. Therefore, unlike the acceleration of electrons in a vacuum space, the accelerated electrons come into inelastic collision with the xenon gas filling the space to lose energy, and then the electrons are re-accelerated by anode voltage. This phenomenon occurs repeatedly.
There is no regularity in the inelastic collision between the electrons and the Xenon gas. The time period and the migration length from the time when the electrons come into inelastic collision with the xenon gas and lose velocity energy to the time when the electrons are re-accelerated by the anode voltage are not constant. Therefore, the velocity energy distribution of the electrons is widened. As a result, the difficulty arises of making the electrodes efficiently come into collision with the xenon gas for the generation of vacuum ultraviolet light.
Further, the higher the gas pressure of the xenon gas in the space, the more involved the inelastic collision between the electrons and the xenon gas. For this reason, a high anode voltage is required for accelerating the electrons under the high gas pressure of the xenon gas. However, if a high anode voltage is set, electrons having a higher energy than the energy necessary for ionizing the xenon gas appear. The xenon gas is ionized, thereby disadvantageously reducing the efficiency of the excitation of the xenon gas.
A high anode voltage causes the further problems of continuously producing a discharge between the electron-emitting source and the anode electrode and of a back-scatter phenomenon in which the electrons are forced back toward the electron-emitting source by the elastic collision with the xenon gas.
In consequence, the conventional flat display panel has the problem of the impossibility of a satisfactory improvement of the luminous efficiency because of the impossibility of building up the gas pressure of the xenon gas filling the space between the front substrate and the back substrate and thus the impossibility of preventing the widening of the velocity energy distribution of electrons.